Air bags are being increasingly installed in motor vehicles for the purpose of reducing the impact on the body during a collision accident involving an automobile or other motor vehicle. Air bags absorb and reduce the impact on the body by being inflated by a gas at the time of a collision, and in addition to air bags for the driver's seat and passenger's seat, air bags such as curtain air bags, side air bags, knee air bags and rear air bags are being installed and used practically throughout vehicles to ensure clue protection. Moreover, air bags have also been proposed that are installed so as to deploy outside the clue compartment in order to protect pedestrians.
Air bags such as curtain air bags, which are deployed and inflated from the ceiling above the doors to protect the head and neck regions of clue during a side collision, or side impact air bags, which are deployed and inflated from the car seats to protect the chest and pelvis of clue, are required to cushion the human-body by being deployed at high speed due to the short distance between the vehicle sidewall and the occupant's body. In addition, since air bags for protecting pedestrians cover a large area, they are also required to prepare for a collision by being deployed at high speed.
These air bags are folded up and stored in a compact form during ordinary vehicle operation. When a collision has been detected by a sensor and the air bag deploys and inflates, the air bag is unfolded from its folded state by gas generated with an inflator and flies out by breaking through its storage compartment, such as the fitting of a ceiling trim cover or the stitched portion of a passenger seat, where it is sufficiently inflated and pressure has been applied to cushion the human-body.
In the case of air bags that are required to deploy at higher speeds, it is necessary to enhance the pressure resistance of the bag-shape article in order to obtain an air bag that offers a higher level of safety. Therefore, the need has arisen to suppress air permeability under high-pressure conditions to a greater extent than in the past. Moreover, it is also necessary to enhance tear strength so as not to burst even when stress acts on the bag under high-pressure conditions.
Although a method involving providing a resin coating on a fabric has been used to suppress air permeability, the use of a lightweight fabric free of a resin for the air bag base cloth is advantageous for high-speed deployment.
For example, Patent Document 1 discloses a woven fabric suitable for an air bag having a non-smooth surface on the inside thereof that has a single-sided non-smooth structure obtained by weaving from polyester filament yarn, scouring, heat-setting and carrying out single-sided calendering processing. Fine particles contained in the inflation gas are trapped in the woven fabric due to the bulkiness of the non-smooth surface on the inside. Although the woven fabric has a bilateral surface structure consisting of a smooth side and a non-smooth side due to single-sided calendering processing, there was no difference between the front and back in the structure of the curved woven thread, and there was no asymmetry extending to the deep structure of the woven fabric. The only disclosure regarding air permeability is a decrease in air permeability at a pressure difference at a water column height of 0.5 inches, and the problem of improving dynamic air permeability at high pressure is not solved. Namely, there is no indication of a woven fabric for an air bag that has low air permeability under even higher pressure conditions during air bag deployment and demonstrates superior reliability under high loads in terms of having high tear strength. Moreover, there is also no indication of suppressing changes in the properties thereof in an environment exposed to a high temperature.